1. Field of the Invention
The invention relates to digital filtering circuitry. More particularly, the invention relates to digital circuitry that filters undesirable or invalid data from data signal lines.
2. Description of the Related Art
Filters and filtering circuitry have many uses in modern electronic devices, circuits and systems. One such use is to recognize or filter undesirable or invalid data on data signal lines. Invalid data includes, e.g., logical state transitions (i.e., low to high and high to low data transitions) whose duration is greater than desired. Conventional filters or other arrangements used to filter invalid data include analog filters, which typically comprise filtering arrangements that include one or more analog components. For example, a conventional RC filter circuit eliminates high to low transitions depending on the RC value. However, in general, it is relatively cumbersome to design and manufacture an analog filter, and the quality and performance of analog filters often depend on the filter manufacturing process. For example, the existence of leakage current and the variability of capacitor and resistor values due to process parameters such as voltage and temperature often greatly affect the operation and performance of analog filters. Moreover, conventionally, it has been relatively difficult to manufacture an analog filter that adequately recognizes or filters invalid data on data signal lines and reduces or minimizes the rise and fall time of the output filtered signal. Accordingly, such conventional filters are unsuitable for use in devices and systems that can not tolerate such delays.
Accordingly, it would be desirable to have available an all-digital circuit that filters invalid data on data signal lines while overcoming the shortcomings of conventional filters including analog filters.